Hoa G. Nguyen's low-cost/low-tech

Freshwater Planted Aquarium

Questions and Answers

The following are some of the responses I have given to various questions through private correspondence and in public forums.

Q: Why don't you have any airpump?

A:
The need for an air pump is a myth. It is not clear whether the real function of the air bubble wands is to produce the air bubbles or to provide a water current on the surface of the tank (caused by the rising bubbles). No definitive tests have been done comparing the aerating effects of having the bubbles vs. the surface current. I believe that any method of generating a surface current will do the job--for example, using a filter with intake and outlet at opposite ends of the tank. If you have that, you don't need an air pump, even without plants.

If you have lots of vigorously growing plants, then their photosynthesis provides more than enough oxygen. When you see oxygen bubbles coming off the leaves (which I see after the lights have been on for an hour or so), then oxygen saturation has been reached in the tank water and no more oxygen can be dissolved. Thus, with a densely planted tank, you don't even need a surface current for aeration. In fact, if you inject CO2, then you do not want a surface current, which will drive off your CO2 (what you need then is a subsurface current to circulate water past the plants). My brother-in-law has a planted tank with no filter and no air pump, just static water with plants, fish and frogs in it. However, you need strong light and CO2 supplementation to have oxygen saturation in a tank.

Q: Should I use bacteria starters to seed my new filter?

A:
All new aquaria need to be cycled. This is a process where a population of bacteria is grown in your new filter to become large enough to handle the conversion of future fish wastes into harmless products. It can be done by slowly adding one or a few fish at a time to your aquarium, or fishless by adding ammonia to the aquarium directly. The initial few bacteria (entered via the air, water or other opportunistic means) multiply over a few weeks into a large enough population. The process can be sped up by seeding the aquarium and filter mdedia (which just provides a greater surface area for bacteria attachment) with live bacteria, by adding some gravel, filter media or water from an established aquarium.

Recently some commercial products have appeared, such as Cycle or Sure-Start, claiming to contain live bacteria (Nitrosomonas and Nitrobacter) that will speed up or eliminate your cycling process. It is very difficult to evaluate their claims, because most people only start up one aquarium at a time, and thus cannot provide "double blind" tests on the effectiveness of such products. There have been one instance reported in the Aquatic Plant Digest of a person who cycled two tanks at the same time, one with Cycle and one without, and directly compared the cycling time between the two (by monitoring ammonia, nitrite and nitrate). He found no difference.

There are two problems with these products, one is the freshness issue mentioned in the article on cycling, and the other is the fact that our previous assumptions about the specific bacteria responsible for the cycling process may be WRONG! Nitrosomonas and Nitrobacter bacteria have traditionally been assumed to perform the function of converting ammonia to nitrate in aquaria. However, they were identified using bacterial culturing techniques that were prone to errors. Dr. Tim Hovanec, using modern RNA analysis, found almost none of these bacteria in mature freshwater aquaria. Instead, he found large populations of Nitrospiras that could be performing these nitrifying functions. His research was published in the scientific literature in 1996 (the August issue of Applied and Environmental Microbiology) and in the December 1996 and January 1997 issues of Aquarium Fish Magazine. If his research conclusions are correct, then these commercial products such as Cycle and Sure-Start are packaging the wrong bacteria! My opinion is that you would be better off saving your money, and just use some water or gravel from an established aquarium to seed your tank.

Q: Since CO2 is heavier than air, wouldn't the injected CO2 that escapes from the aquarium form a layer on top of the water and prevents O2 from entering?

A: This question was debated on the Aquatic Plant Digest for a while. Some people said yes and cited incidents where CO2 collected at the bottom of large caves or vocano craters, and suffocated people and animals in them. Intuition said that this cannot happen in an aquarium, or else there would be a serious deficiency of O2 in the water at night, when plants are not synthesizing. I went back to college physics textbooks and did some research. The conclusion I came up with was that there would not be a distinct layer of CO2 on the water surface. The reason is that the distribution of the heavier gas (CO2) in a volume of lighter gasses (air) in the presence of gravity is based on a gradient. The percentage of CO2 at the bottom is higher than the percentage of CO2 at the top, but the decrease is gradual (a gradient). The magnitude of the gradient (or rate of change) depends on temperature--the colder it is, the greater the gradient (colder gas molecules do not jump around as much, and thus settling down more).

In a cave or at the bottom of a vocano, chances are the temperature is low and the vertical distance is so great that at nose level, the concentration of CO2 is very high and the concentration of oxygen is too low to support life. In comparison, the temperature in the airspace above the aquarium water is higher, thus the gradient is lower, plus the space between the aquarium water surface and the top of the tank is very small, so the concentration of CO2 at the water surface and at the top of the enclosure is for practical purposes the same. That is, the CO2 is distributed evenly in the airspace between the aquarium water surface and the top of the tank. Thus CO2 will readily escape through any opening at the top of the tank.

A: The Kelvin temperature is an approximation of the color of the light (the higher the bluer, the lower the redder). It is supposedly the color of light that a black body (a piece of metal) will radiate if heated to that temperature, but it's not very precise when applied to lamps other than incandescent. It does not say anything about the spectrum of the light. Many entirely different spectra may produce the same color tone. For example, the following three spectral distributions all look yellow (from Hurvich, L.M., "Color Vision", 1981):

A peak at 580 nm

A gradual, linear rise from 470 nm to 700 nm

A low peak at 570 nm combined with a peak at 700 nm

So, the difference between 10,000K and 3,000K degrees shows up most as the color of your tank. You can't say if a bulb is good for plants from just the color temperature. Daylight is about 5500K color temperature. However, there are daylight bulbs that are triphosphor/trichromatic (with 3 peaks in the spectrum, such as the GE Daylight Ultra) and other daylight bulbs that are full or broad spectrum (such as the Philips Daylight Delux)--see my Fluorescent Light Comparison page.

A:Actually, Malaysian Trumpet Snails are considered pests by the fish stores. They aren't usually for sale, but often are found in their tanks. If you find them in the tanks, just ask the store clerks if you could have a few. They may give them to you for free, or charge a nominal fee for the work to bag them for you.

For other helpful notes relating to aquarium and fishkeeping, see my Comments page.